There is a known endoscope in the related art in which marks indicating the distance from the tip of an insertion portion are provided on the outer surface of the insertion portion for ascertaining the insertion depth of the insertion portion of the endoscope, and which is equipped with a reading device for reading these marks (for example, refer to Patent Documents 1 to 3).    Patent Document 1: Japanese Unexamined Patent Application, Publication No. SHO-55-116330    Patent Document 2: Japanese Unexamined Patent Application, Publication No. HEI-6-90899    Patent Document 3: Japanese Unexamined Patent Application, Publication No. 2004-105725